The present invention is related to an optical information recording medium, and in particular to a rewritable optical recording material, which undergoes a phase change between the crystalline and amorphous states upon irradiation of a signal laser beam, thus enabling recording, erasing, reproduction and over-writing and the rewritable optical disks thereof.
An erasable phase-change optical disk utilizes a phase change between the crystalline and amorphous states of a recording layer to accomplish the functions of writing and erasing. The working principles of the erasable phase-change optical disk will be introduced in conjunction with typical prior art references hereinafter for a better understanding of the present invention.
A typical erasable phase-change optical disk is shown in FIG. 1, which comprises a phase-change recording layer 2 interposed between an upper dielectric layer and a lower dielectric layer 3 on a substrate 1, a reflective layer 4 on the upper dielectric layer, and a plastic protection layer 5 on the reflective layer 4. A suitable material for making the dielectric layers 3 is SiO2xe2x80x94ZnS. The substrate 1 may be formed of polymethyl methacrylate, polycarbonate or a glass. Suitable materials for forming the reflective layer 4 include Au, Cu, Al, Ni, Cr, Pt, Pd and an alloy thereof.
The currently used erasable phase-change optical disks utilize a chalcogenide material based on Te or Se as the recording layer. When a region of the recording layer is subjected to a rapid heating to a molten state upon irradiation of a focused laser beam with a high power short pulse modulation, the region will be conductively quenched by the adjacent layers (e.g. the dielectric layers and reflective layer) to an amorphous state, so that a recording mark is formed. The amorphous recording mark has a reflectance lower than that of the blank crystalline region (for some special alloys the reflectance of amorphous recording mark is higher), and the difference in reflectance is used for reproduction of signals. A medium power and long pulse laser beam is used to erase the recording mark, which resumes the blank crystalline region by heating to a temperature between its melting point and crystallization point.
The chalcogenide material was first used as the phase-change recording layer by S. R. Ovsinsky, et al. in U.S. Pat. No. 3,530,441, wherein thin films of Te85Ge15 and Te81Ge15S2Sb2 produce a reversible phase-transition according to irradiation with high energy density light such as the laser beam. Thereafter, most of the research works have concentrated on the chalcogenide materials, for examples GeTe, InSe, InSeTI, InSeTICo, GeSbTe, GeTeSn, GeTeAs, GeTeSnAu, InTe, InSeTe, InSbTe, and SbSeTe, etc. all pertain to the chalcogenide material. Among them, the series of GeSbTe alloys developed by Matsushita Electric Industrial Co., Ltd., Japan, in U.S. Pat. Nos. 5,233,599; 5,278,011; and 5,294,523 are the most promising ones. The details of these patents are hereby incorporated by reference in their entirety.
However, the aforesaid phase-change materials have a common drawback, which is the existence of two crystalline phases during the crystallization thereof, i.e. the low temperature FCC (face-centered cubic) phase and the high temperature HCP (hexaganol close-packed lattice) phase. A phase transition between the FCC and HCP significantly reduces reliability of the rewritable phase-change optical disk after a long period of use, and decreases the feasible number of writing-erasing cycles.
The present invention discloses a novel series of five-element alloys, Texe2x80x94(Ge,Bi,Sb)xe2x80x94X, X=B or C, for use as a phase-change optical recording material that shows improvements over those of the prior art. Typical improvements of the five-element alloys of the present invention comprise an excellent high crystallization rate, and a high optical contrast between the amorphous and crystalline states within the visible light range, and thus is very suitable for use as a rewritable phase-change optical recording material.
A rewritable phase-change optical recording composition designed according to the present invention is to replace part of Ge in the Texe2x80x94Ge binary system with Bi and Sb simultaneously, and further dope small atom boron or carbon, which has the following formula:
[Te (Ge1-xcex1Mxcex1)xcex3]100-aXa
wherein M=Bi1-xcex2Sbxcex2, X=B or C, or more explicitly, expressed in atomic percentage (at. %):
[TexGexcex3(Bi1-xcex2Sbxcex2)z]100-aXa
wherein x=47xcx9c60 at. %; y=12xcx9c48 at. %; z=5xcx9c41 at. %, x+y+z=100 at. %; xcex2=0.1xcx9c0.9; and a=0.05xcx9c4 at. %.
The rewritable phase-change optical recording compositions of the present invention may be classified into two groups according to the value of y, wherein the first group compositions have y=28xcx9c48 at. %, z=5xcx9c25 at. %, xcex2=0.1xcx9c0.9, and a=0.5xcx9c3 at. %; and the second group compositions have y=12xcx9c28 at. %, z=12xcx9c41 at. %, xcex2=0.1xcx9c0.9, and a=0.5xcx9c3 at. %.
Preferably, the first group compositions have an optical contrast between the amorphous and crystalline states greater than 30% within a visible light range.
Preferably, the first group compositions have a crystallization temperature ranging from 180 to 210xc2x0 C.
Preferably, the first group compositions only have the face-centered cubic (FCC) phase in its crystalline state and at a temperature below 300xc2x0 C.
Preferably, the first group compositions have a crystallization activation energy ranging from 1.5 to 3.5 eV at the crystallization temperature.
Preferably, the second group compositions have an optical contrast between the amorphous and crystalline states greater than 20% within a visible light range.
Preferably, the second group compositions have a crystallization temperature ranging from 140 to 180xc2x0 C.
Preferably, the second group compositions only have the face-centered cubic (FCC) phase at a temperature below 250xc2x0 C.
Preferably, the second group compositions have a crystallization activation energy ranging from 1.5 to 3.5 eV at the crystallization temperature.
Preferably, the first group compositions have the following compositions: (Te50.6Ge37.4Bi5.7Sb6.3)99.11B0.89, (Te50.6Ge37.4Bi5.7Sb6.3)98.46B1.54, (Te50.6Ge37.4Bi5.7Sb6.3)98.14B1.86 or (Te50.6Ge37.4Bi5.7Sb6.3)99.01C0.99.
Preferably, the second group compositions have the following composition: (Te54.5Ge22.0Bi6.5Sb17.0)99.26B0.74, (Te54.5Ge22.0Bi6.5Sb17.0)98.73B1.27, (Te54.5Ge22.0Bi6.5Sb17.0)98.15B1.85 or (Te54.5Ge22.0Bi6.5Sb17.0)98.93C1.07.
The present invention also provides a rewritable phase-change optical disk comprising a substrate; a rewritable phase-change optical recording layer deposited on said substrate, wherein said rewritable phase-change optical recording layer has a composition of said rewritable phase-change optical recording composition of the present invention.